Base station antenna deployment has generally been done with passive antennas, such as fixed electrical tilt (FET), mechanical electrical tilt (MET), and remote electrical tilt (RET) antennas. Over the years, the increased use of spectrum has resulted in increased complexity starting from mostly single band FET antennas gradually moving to multiband RET antennas. However, these antennas are passive antennas, and do not contain any active RF devices such as amplifiers and radios within the antenna. Therefore, these antennas still have significant RF losses from the radiating element to the first active device. For example, the first active device can be a NodeB, a Tower Mounted Amplifier (TMA), or a Remote Radio Head (RRH). The magnitude of these RF losses can be in the order of several dB, which can significantly affect system performance.
In active antenna environments, RF losses disappear because active devices, such as low noise amplifiers (LNAs) in the uplink path or power amplifiers (PAs) in the downlink path, are brought into as close as possible to the antenna radiating element. The proximity of the antenna radiating element to the active devices mitigates many of the losses associated with passive antenna radiating elements, such as feed network losses, phase shifter losses, and cable feeder losses. The beam can be then formed with an electronic phase shifter, in the analog or digital domain.
In an active antenna, an array of broadband radiating elements can be combined with distributed modules. Each distributed module may contain a double triplexer, double LNA, double PA, phase shifters and attenuators, and may also be combined with a passive feed network, with a passive phase shifter. These modules are compact and essential building blocks of the all antennas. While operators are very pleased with the improved performance that can be brought by active antennas, the challenge remains when multiple technologies, such as second generation air interface standards (“2G”), third generation air interface standards (“3G”), and fourth generation air interface standards (“4G”) are combined on the same tower, or on the same antenna due to tower loading and zoning restrictions.